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Cat's Eye Nebula--the death shroud of a star much like our Sun (but not for 5 billion years): courtesy STScI-Hubble/CXO-Chandra
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Humans used to think we lived at the still center of a turning Universe. Earth was static, and the stars spun overhead. Humanity was the measure of all things. Some revolutionary Greek thinkers like Aristarchus of Samos were the first to think that perhaps this was incorrect, but it was not until the Polish cleric, Nicholas Copernicus, published his book in 1543, DE REVOLUTIONIBUS, (check and hot link to some online source) that the idea re-emerged in Western thinking with a more developed sets of arguments to buttress it. The Copernican revolution (pun intended) said that Earth orbited the Sun, and the implications of his ideas--as built on by Galileo and others--was that Earth was in no privileged position, and that humanity was not at the center of creation. In the centuries since then, a number of additional revolutions in thought have made us believe that the Universe is both far more immense and far older than Copernicus and many of his contemporaries ever imagined. But this new Universe is just as much our home as the Earth-centered model believed true in the centuries before Copernicus. It's amazing that our minds can reach out and comprehend the forces that made us and our world.
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EO102--a supernova remnant unusually rich in oxygen, enough to give several solar systems like ours the stuff of life. (Chandra X-ray image)
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We now believe that life on Earth began relatively soon after (perhaps 2-300 million years!) our solar system formed, from a spinning cloud of gas and dust, some 4.5 billion years ago. The elements that make our bodies, in turn, were created in massive supernova explosions that pre-dated that long-gone epoch, when an earlier generation of stars used up their hydrogen and other fuels and imploded, scattering the oxygen we breathe and the iron in our blood across the Galaxy. We are literally, as the late astronomer Carl Sagan said, all star-stuff. And it turns out that cosmic evolution continues today.
